The colors in an image can be determined, not only by the colors of objects in the scene being imaged, but also by the colors used to illuminate the objects in the scene. Photographers often take advantage of this, e.g., by using low-color-temperature light to make skin tones appear warmer. On the other hand, if an image is to represent the actual colors of an object, illumination color can be carefully controlled. For example, document scanners use carefully specified illumination sources to achieve known effective color temperatures. In addition, typical document scanners employ covers to exclude ambient light (which is less likely to be controlled) from the object being scanned.